(CNN) -- Delta Air Lines and American Airlines announced Thursday the cancellations of hundreds of flights so the companies can conduct inspections on bundles of wires in some of their jets.

The cancellations will affect flights through Friday, according to statements by both companies.

A spokeswoman for Delta earlier said 325 flights would be canceled Thursday, but later said 275 flights were cut.

"Delta apologizes in advance for any inconvenience this may cause and is working to proactively contact and reaccommodate affected customers. Customers should call ahead to check flight status," a Delta statement said.

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Wednesday, American Airlines canceled 318 flights, said company spokesman Tim Wagner. The airline canceled 132 of its estimated 2,300 flights scheduled for Thursday, Wagner said, about 6 percent of the daily schedule.

The cancellations forced dozens of people to spend the night in the atrium of Atlanta's Hartsfield-Jackson International Airport. They slept wherever they could -- on couches, on the floor, some on non-moving baggage carousels.

Kelly said the airline rebooked flights and covered the cost of hotel and food for passengers on canceled flights.

It was initially believed that Delta's MD-90 planes were part of the inspection but it was determined that the MD-88 planes were the only ones that needed to be inspected, a spokeswoman said. The airline said the checks are voluntary and are expected to be completed by week's end. American Airlines, meanwhile, is examining wiring secured to its MD-80 aircraft.

In Atlanta, the cancellations caused grousing among passengers who missed job interviews, connecting flights and the comfort of their beds, CNN affiliate WXIA reported.

"They told us 6:45 (p.m.). Then they told us 7:30. Then 8, so on and so forth and they just canceled," passenger Fred Billizon told WXIA. "So they had about 200 people just waiting on flights. And that's not a lot of happy people."

This latest round of inspections was prompted by questions raised by the FAA and American safety officials about how a certain bundle of wires is secured to the MD-80 aircraft.

The MD-80 is the workhorse of the American fleet. American's Web site says the aircraft accounts for 300 of the airline's fleet of 655 jets.

The jet debuted in 1980 from McDonnell-Douglas, which was purchased by rival Boeing in 1997. Boeing discontinued production of the aircraft in 1999.E-mail to a friend